Gas turbine engines are used to power aircraft, watercraft, power generators, and the like. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high-pressure air to the combustor. In the combustor, fuel is mixed with the high-pressure air and is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft. Left-over products of the combustion are exhausted out of the turbine and may provide thrust in some applications.
Mechanical power is transferred from turbines to compressors through shaft and spline systems, with bearings providing axial and radial positioning of the rotating components. A central shaft (which may be referred to as a “main” shaft, a “main drive,” or a “mainline” shaft, for example) typically links the turbine and compressor sections of the turbine engine. In turbine engines having multiple turbine and compressor sections, there may be multiple, concentric, independently rotatable shafts. For example, a high-pressure shaft may link a high-pressure compressor with a high-pressure turbine, while a low-pressure shaft links the fan with a low-pressure turbine. The low-pressure shaft may be concentric with and disposed within the high-pressure shaft. Certain maintenance procedures may require inspecting and verifying the condition of one or more shafts, which may require taking the engine of service and disassembling the engine.